"This is a shock," said Judy Arnold, president of the Board of Supervisors, adding officials were scrambling to determine what could be done to fill the gap.

At issue is a roughly 10 percent cutback in funds benefiting 2,100 families enrolled in the Section 8 rental subsidy program, most in San Rafael and Novato. Cuts loom for administration and other housing programs as well.

County housing chief Lewis Jordan said that as "specifics are trickling in from Washington about the automated cuts known as the sequester, it is clear that the Marin Housing Authority will need to reduce its services."

"The across-the-board national funding cuts will affect Marin County residents regardless of their economic vulnerability," Jordan said, adding that many of those affected are elderly or disabled.

County officials are seeking an emergency grant while Lewis hurdles legal complexities as he tries to determine how to proceed in a way that benefits most of those involved.

"We're going to speak to the Marin Community Foundation to see if they can provide a glide path," Arnold said. "It's important for us to fill the gap" pending deliberations in Washington D.C. that will determine the extent of future funding, she said. "We don't know if this is a short-term problem" or a permanent cut.

Next fiscal year's county budget includes a $5 million reserve fund earmarked to help ease federal and state budget cuts.

Thomas Peters, CEO of the community foundation, said Wednesday that he had not yet conferred with the county about the funding crisis. "Sounds as if the slowly-building sequester tsunami is rolling in," he noted.

The housing cutbacks affecting Marin's poor appear to be among the most significant local impacts so far after the failure of Congress to reach a budget accord.

"The details have not been ironed out, but the cuts will impact Marin housing's two largest programs — housing choice voucher and public housing," Jordan reported. Because the housing authority has annual contracts with 1,600 landlords that lock in rent payments, the cuts will affect tenants, some of whom could see rents double. Tenants now pay rent based on their earnings, generally about 30 percent of income, and federal subsidies pick up the rest.

In a letter to rent subsidy tenants, Jordan explained that officials are studying ways to "retain as many families as possible in the housing voucher program," including reducing "our current payment standards" by hiking tenant rents.

"I'm running numbers how to determine how much more tenants will have to pay," Jordan said, noting the pinch could be shared by landlords over the next year as leases expire.

What Congress will do is anybody's guess, Jordan said. "I'm not sure Washington knows what is going on," he added.

Rep. Jared Huffman, D-San Rafael, could not immediately be reached for comment, and a spokeswoman at the San Francisco office of the federal Department of Housing and Urban Development had no information on the extent of cutbacks in the state or elsewhere, saying the situation in Washington was "fluid."

The Marin County Housing Authority operates with a $30 million budget and 50-member staff that provides housing assistance to 10,000 Marin residents.